1. Field of the Invention
This invention relates generally to the field of non-destructive inspection (NDI) of structures and more particularly to a hand held positioning and control device for imaging arrays such as Magnetoresistive (MR) scanning arrays.
2. Description of the Related Art
Non-destructive inspection (NDI) of aerospace structures to detect flaws may be performed by various techniques that include X-ray radiography, ultrasonics, acoustic emissions, and eddy currents. Current imaging scanners are typically operated using mechanical positioning means which require significant mechanical and structural support. Currently there is no hand held device that can rapidly scan along a row of fasteners to inspect the subsurface condition of the structure.
Eddy current inspection devices are commonly used for NDI of electrically conductive components. Eddy current inspection devices typically use one or more excitation coils to generate an alternating magnetic field, which in turn induces eddy currents in the component, and typically use a pickup coil to detect the magnetic field generated by the eddy currents. When an eddy current encounters an internal flaw of the component, the eddy current flows around the flaw and the resulting magnetic field generated by the eddy current is changed. The pickup coil indirectly detects this change which gives information regarding the location and size of the flaw within the component.
Magnetoresistive (MR) sensors are known for low frequency performance permitting deep feature/flaw detection in metallic structure at sensitivities considerably above those provided by conventional eddy current techniques. Exemplary NDI systems employing MR are disclosed in U.S. Pat. No. 6,150,809 to Tiernan et al. which uses two parallel sheets of conductors to create the magnetic field and uses a giant magnetoresistive (GMR) sensor positioned between the sheets to detect the magnetic field signals generated by eddy currents and application Ser. No. 10/923,519 entitled EDDY CURRENT INSPECTION DEVICE, having a common assignee with the present invention, the disclosure of which is incorporated herein by reference.
Eddy current inspection using MR sensors is applicable to scanning of specific structural elements on an aircraft, containing rows of rivets or other fasteners. It is therefore desirable that an imaging scanner be mounted in a structure for operation by hand to allow a technician to accurately yet conveniently perform inspection of the desired structure.